Method and apparatus for cutting sheet material

ABSTRACT

A method and apparatus for cutting sheet material utilize a reciprocating cutting blade that is guided through a layup of sheet material along a cutting path defining the periphery of a pattern piece. The cutting blade is positioned generally perpendicular to the sheet material being cut and bears a cutting edge which is advanced through the sheet material as the blade is reciprocated. The stroking speed of the reciprocating cutting blade is regulated as the cutting blade advances to prevent excessive heat from being generated due to the frictional contact of the reciprocating cutting blade and the sheet material. Along sections of the cutting path which permit rapid advancement of the cutting blade, the stroking speed is increased to optimize the cutting operation without generating excessive heat and thereby fusing the sheet material. At other sections of the cutting path where the rate of advancement is decreased, the stroking speed is also decreased to reduce local heating and fusion.

United States Patent [1 1 Gerber Dec. 25, 1973 METHOD AND APPARATUS FORCUTTING SHEET MATERIAL [75] Inventor: Heinz Joseph Gerber, WestHartford, Conn.

[73] Assignee: Gerber Garment Technology, Inc.,

East Hartford, Conn.

[22] Filed: Jan. 3, 1972 [21] Appl. No.: 214,579

Primary Examiner.l. M. Meister Attorney-John C. Linderman [5 7 ABSTRACTA method and apparatus for cutting sheet material utilize areciprocating cutting blade that is guided through a layup of sheetmaterial along a cutting path defining the periphery of a pattern piece.The cutting blade is positioned generally perpendicular to the sheetmaterial being cut and bears a cutting edge which is advanced throughthe sheet material as the blade is reciprocated. The stroking speed ofthe reciprocating cutting blade is regulated as the cutting bladeadvances to prevent excessive heat from being generated due to thefrictional contact of the reciprocating cutting blade and the sheetmaterial. Along sections of the cutting path which permit rapidadvancement of the cutting blade, the stroking speed is increased tooptimize the cutting operation without generating excessive heat andthereby fusing the sheet material. At other sections of the cutting pathwhere the rate of advancement is decreased, the stroking speed is alsodecreased to reduce local heating and fusion.

12 Claims, 7 Drawing Figures PATENTEUU I973 .SHEEI10F3 FIG. 3

FIG. 2

PATENTEDDECZ 51015 SHEET 2 0F 3 MARKER 80 FIG. 4 I I I BASIC @UCZCOMMANDS 2 I I I DIGITIZER DATA RECORDER TAPE CONTROLLER PROCESSOR 82 lPOINT BASIC CUTTING CONTROLLER e DRIVER 9 /I4O I44 I36 MOTOR X T SHAPERSTROKE CIRCUIT DRIVER l 70 I42-- I \Y RATE /G i |3O 44 STROKI l MOTOR xDRIVER x MOTOR -1 -|32 I J Y DRIVER Y MOTOR I4 /-2O FIG. 6

CONTROLLER 9 DRIVER I I36 7O STROKE STROKING MOTOR x DRIVER x MOTOR r II I I32 I 54 l Y DRIVER Y MOTOR PAIENIEDUEBESIS'YS FIG. 5

CHANGE IN DIRECTION ENTRY REDUCE SPEED I /'IO6 I STOP FEED I REDUCESPEED 00 EXIT I I j I FEED PROPORTIONAL 98 I TO AX,AY --1I YES /II2 IEXIT mz FEED, SPEED NO PROPORTIONAL ,95

TO Ax,AY I z1 l. FEED RATES I EXIT -ll4 I 2. STROKING SPEEDS I I3.HARDWARE LIMITS I 5. AD ,AD I 1 I I I I II6 I DOES I MAX. FEED YESEXCEED HARDWARE I I LIMITS II8 I REDUCE FEED, SPEED EXIT 2O EXIT METHODAND APPARATUS FOR CUTTlNG SHEET MATERIAL BACKGROUND OF THE INVENTION Thepresent invention relates to method and apparatus for cutting sheetmaterial. More particularly, the present invention relates to the methodand apparatus in which a reciprocating cutting tool is driven at aregulated stroking speed as the blade is advanced or guided along a lineof cut through a layup of sheet material such as that utilized formanufacturing upholstery, garments or the like.

The use of automatic control equipment for cutting large numbers ofpattern pieces from sheet material, such as fabrics from which wearingapparel, upholstery and other articles are made, is already well-knownin the art as indicated in US. Pat. No. 3,495,492 entitled Apparatus forWorking On Sheet Material" and assigned to the assignee of the presentinvention. In cutting mechanisms of this type, a reciprocating cuttingblade is generally stroked in a direction normal to the sheet materialas the cutting edge of the blade is advanced or guided along apredefined cutting path by a digital or analog controller. Thecontroller derives basic commands from a memory device such as a punchedor magnetic tape on which a cutting program is recorded. As the tape isread, the controller interprets the basic commands and causes thecutting blade to be operated and to move along a desired line of cutdefining the periphery of a pattern piece in cutting engagement with thefabric layup. Because of the speed and accuracy with which automaticcutting equipment cuts out a plurality of pattern pieces from multi-plylayups of fabric sheet material, such cutting mechanisms have receivedfavorable acceptance in the apparel industry where large quantities ofpattern pieces are desired.

When a reciprocating cutting blade plunges into a layup of fabricmaterial and advances along a line of cut with a chopping blade stroke,that is a stroke which causes the blade to be withdrawn and plunged backinto the material during each reciprocation cycle, it is necessary toinsure that the reciprocation rate is sufficiently high so that theforward motion of the blade does not out run the stroking of the bladeand produce what is sometimes called in the trade stitching/Duringstitching," the fabric material is not completely severed at each pointalong the line of cut because the cutting blade is advanced too rapidlyduring a single reciprocation of the blade and allows the material topass under the blade as it is withdrawn without being cut. Theparameters which determine the uppermost limit at which a reciprocatingblade can be advanced without stitching are the width of the blade, thestroke of the blade and the reciprocation rate. The chopping bladestroke, rather than a shorter stroke which leaves the cutting blade inthe material at all times, is preferred, particularly with thermoplasticvinyls and similar materials that have low fusing temperatures, becausethe guide or sheath within which the blade reciprocates is brought incontact with a greater portion of the cutting blade during eachreciprocation cycle and permits heat generated by friction between theblade and the material to be transferred away from the blade.Accordingly, there is improved heat transfer and less opportunity forfabrics to be heated to elevated temperatures and to fuse as the cuttingblade advances along the line of cut.

it will be understood that to avoid stitching" in a cutting mechanismhaving a fixed reciprocaton rate and stroking speed, the stroking speedof the cutting blade must be selected for the maximum speed ofadvancement of the cutting blade through the sheet material. The drivemotor and drive train for stroking the cutting blade are, therefore,designed in accordance with the maximum speed of advancement of thecutting blade and, in the past, the blade was driven at the designedspeed at all times. In selecting a fixed reciprocation rate, it isnecessary to keep in mind the fact that certain materials fuse when thereciprocation of the cutting blade produces excessive heat in the fabriclayup. Local hotspots along the cutting path may be generated where theblade advancement is interrupted or where the rate of advancement of thecutting blade is reduced due to limitations of the cutting mechanism.For example, when the cutting blade is guided around curves having ashort radius or is advanced along a very short path segment, it iscustomary to reduce the feed rate of the cutting blade to maintainaccurate tracking of the cutting path and to prevent undue wear on themechanical components of the cutting mechanism. If the designedreciprocation rate of the cutting blade is high in order to make rapidtraverses along straight sections of the cutting path, it is possiblethat at localities along the cutting path where the feed rate is reducedexcessive heat will be generated in the layup due to the prolongedfrictional contact between the layup and the rapidly reciprocatingblade. The excessive heat can cause fusion between the different pliesof the layup and also across the cut so that the pattern pieces are notentirely severed from each other and from the remnant fabric. Inaddition, the material itself may be damaged and thereby rendereduseless for its intended end product. It will be understood that acompromised reciprocation rate providing a useful high speed traverseand avoiding fusion at low feed rates must be obtained in a system inwhich the cutting blade is driven at a constant stroking speed, and thatthe performance of the cutting mechanism in such a system may not beoptimum.

In accordance with the present invention, a cutting system is disclosedin which the cutting blade is reciprocated at an adjustable strokingspeed and the stroking speed is regulated as the blade advances alongthe path in accordance with the feed rate of the blade and the materialor the geometry of the cutting path.

SUMMARY OF THE INVENTION The present invention resides in a method andapparatus for cutting a layup of sheet material along a path definingthe periphery of a pattern piece. A cutting blade having a cutting edgeextending along the leading edge of the blade is reciprocated in adirection generally parallel to the cutting edge and perpendicular tothe sheet material in the layup by stroking means such as a variablespeed motor and crank linkage. Controlled drive means for moving thereciprocating cutting blade and the layup relative to one another causesthe cutting edge of the blade to move along the cutting path in cuttingengagement with the material in the layup at a controlled feed rate. Thedrive means for moving the blade also includes means for rotating thecutting blade about an axis extending in the same direction as thecutting edge in order to maintain the blade generally aligned in thefore and aft direction with the direction of out along the path. Thestroking means for reciprocating the blade is connected to strokingcontrol means for regulating the stroking speed of the reciprocatingblade as the blade is moved along the cutting path. The stroking speedis generally adjusted to increase with increasing feed rates and todecrease with descreasing feed rates. The cutting apparatus employingthe control means for regulating the stroking speed is a more versatiledevice in that the full capacity of the apparatus is utilized. Highspeed traverses can be executed with a chopping blade stroke withoutstitching" and the blade moves at slow speed along difficult contours inthe cutting path without generating excessive heat and causing fusionbetween the plies of the layup.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of acutting apparatus embodying the present invention.

FIG. 2 is a fragmentary cross-sectional view of the cutting apparatus inFlG. l taken along a line of cut and showing the reciprocating cuttingblade in cutting engagement with a fabric layup on a cutting tablehaving a penetrable bed.

FIG. 3 is a fragmentary plan view of a layup and a typical cutting pathsegment which is traversed by the cutting blade.

FIG. 4 is a block diagram showing a generally complete cutting system bywhich the present invention is practiced.

FIG. 5 is a flow diagram of the logic contained within the dataprocessor in FIG. 4.

FIG. 6 is a schematic diagram of one embodiment of the apparatus in thepresent invention.

FIG. 7 is a schematic diagram of another embodiment of the apparatus inthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show generallythe cutting apparatus which performs a cutting operation in a layup ofsheet material in accordance with the present invention. The apparatus,generally designated 10, is comprised of a cutting table 12, a cuttingtool taking the form of a reciprocating cutting blade 14, a carriagemechanism composed of an X carriage l6 and a Y carriage 18 fortranslating the cutting blade 14 in the X and Y directions respectivelyover the cutting table 12 and a controller 20 which produces cuttingcontrol signals from a cutting program on a memory tape 22. Basiccommands on the tape 22 are converted by the controller 20 into thecontrol signals. The control signals are transmitted through a controlcable 24 to the X carriage l6 and are distributed to various componentson the carriages 16 and 18, including the drive motors for the blade 14,to cause the desired pattern piece to be cut from a layup L of sheetmaterial supported on the table 12. The sheet material may be used formaking wearing apparel or upholstery and the like.

The cutting table 12 contains a penetrable bed 26 defining the supportsurface on which the sheet material is spread in the layup L. Thepenetrable bed 26 may be formed from a material such as styrofoam blocksor bristled mats which permit the cutting blade 14 to reciprocate in adirection perpendicular to the support surface and the sheet materialspread thereon and into the penetrable bed to completely sever the sheetmaterial throughout the entire depth of the layup as indicated in FIG.2. The bed 26 may also be provided with a vacuum holddown system havinga plurality of channels 30 which extend through the penetrable bed to avacuum chamber 32 within the table frame. An overlay 34 of an imperviousmaterial such as a polyethylene sheet is spread over the layup and bydrawing a vacuum through the channels 30, a subatmospheric pressure isgenerated at the support surface of the table i2 and, in conjunctionwith the overlay 34, causes the layup L to be held in a compressedcondition. For a more detailed description of a cutting table havingsuch a construction, reference may be had to U.S. Pat. No. 3,495,492entitled Apparatus For Working On Sheet Material" and having the sameassignee as the present invention.

The carriage 16 is mounted on a pair of gear racks 40, 42 which extendlongitudinally along the edge of the work table 12 in the indicated Xdirection. The carriage 16 has an X drive motor 44 which is connected indriving engagement through pinions (not shown) with each of the gearracks 4b, 42 so that the X carriage 16 can translate in the X directionback and forth over the table 18. The Y carriage i8 is mounted from theX carriage 16 by means of a guide rail 50 and lead screw 52 which extendin parallel relationship between opposite lateral ends of the X carriage16. A Y drive motor 54 is connected in driving relationship to the leadscrew 52 and the screw 52 is threadably engaged with the Y carriage R8in order to shift the carriage 18 in the indicated Y direction relativeto the X carriage 16 and the table 12. Composite motions of the X and Ycarriages l6 and l8 parallel to the work surface of the bed 26 permitthe cutting blade 14 to be translated to any desired location over thelayup L spread on the table 12.

The cutting blade 14 is suspended from the projecting end of the Ycarriage 13 by an adjustable platform 60. The platform 60 can beadjusted in a direction perpendicular to the work surface of the bed 26so that the cutting blade 24 can be raised or lowered between anelevated position in which the cutting blade is spaced above the layup Land a lowered or work position in which the cutting blade reciprocatesin cutting engagement with the layup and penetrates into the bed 26 asindicated in FIG. 2. The cutting blade 14 extends downwardly from theadjustable platform 60 in generally perpendicular relationship with thework surface and the layup L of sheet material and is held in a chuck 62rotatable relative to the platform 60 about a vertical or 6 axis alsoperpendicular to the work surface. The d-rotations of the chuck 62 andthe cutting blade 14 are produced by a 6drive motor 64 and a belt andpulley system 66 connecting the motor 64 to the supporting chuck 62 forthe cutting blade. Rotation of the cutting blade about the 0 axispermits the cutting blade to be translated along a cutting path alignedin the fore and aft direction with the line of cut at each point alongthe path. All of the drive motors 44,54 and 64 receive control signalsduring a cutting operation from the controller 20 to move the cuttingblade M along the desired line of cut in cutting engagement with thesheet material of the layup.

A variable speed stroking motor 70 connects through a crank or eccentricdrive linkage 71 similar to the linkage shown in U.S. Pat. No. 3,477,322to the cutting blade 14 in order to reciprocate the cutting bladethrough the sheet material and the work surface of the bed 26 as theblade is advanced along the cutting path by drive motors 44 and 54.Control signals for regulating the speed of the stroking motor 70 arealso derived from the tape program 22 by the controller 20 as describedin greater detail below. The stroke of the cutting blade produced by themotor 70 and drive linkage 71 is preferably a chopping blade stroke inwhich the cutting blade is lifted entirely out of the layup L duringeach reciprocation cycle. A presser foot 72 most clearly seen in H6. 2and having a central aperture 74 through which the blade reciprocates isalso suspended from the adjustable platform 60 and slides over theoverlay 34 covering the layup L. The presser foot 72 prevents the sheetmaterial from being lifted with the blade 14 during the up-stroke and,therefore, assists the blade during the cutting operation. The blade 14has a sharp, knife edge extending along the leading edge 76 which isadvanced in cutting engagement with the layup material along theprogrammed line of cut. The trailing edge 78 or heel of the blade 14 isgenerally not sharpened but may be if desired. The lower end of theblade 14 also contains two angled knife edges 80, 82 which permit theblade to be plunged through the sheet material to begin a cuttingoperation at any point on the layup L. Also, the knife edges 80, 82assist the blade in penetrating the layup during each reciprocationcycle when a chopping blade stroke is used.

In accordance with the present invention, basic commands defining theline of cut to be followed during the cutting operation are derived fromthe tape 22 and translated by the controller 20 into movements of thecutting blade along the programmed line of cut while the stroking speedof the blade is regulated to optimize the cutting operation. Theoptimization is achieved principally by increasing the cutting speed asthe feed rate increases along generally linear portions of the cuttingpath to prevent stitching and by reducing the stroking speed as the feedrate decreases along relatively short or irregularly shaped segments ofthe cutting path to prevent fusion of the material or excessive heatingof the blade and the material.

A typical portion of a programmed cutting path is shown in a plan viewof the layup L in FIG. 3 for the purpose of explaining the various feedrate changes that are commonly encountered in a cutting operation andthe manner in which the stroking speed is adjusted in accordance withthe present invention. The blade 14 is shown advancing toward point Aalong a generally straight segment of the cutting path P. Until theblade is very close to point A, the blade 14 can travel toward the pointA at the maximum feed rate of the carriages l6 and 18 without exceedingthe hardware limitations, such as acceleration rates associated with theX, Y and 0 control axes, and without causing undue wear to themechanical drive components because the changes in the controlparameters are relatively small from point to point along the cuttingpath. In the prior art cutting mechanisms, the maximum programmed feedrate may be limited by the compromised stroking speed which may bereduced below the maximum obtainable stroking speed to prevent excessiveheating in material at low feed rates. In accordance with the presentinvention, the stroking motor 70 is regulated by the memory tape programto produce the maximum reciprocation rate or at least a ratecommensurate with the maximum feed rate without stitching" so that thedisplacement of the blade per reciprocation cycle does not exceed thewidth of the blade between the leading and trailing edges. Preferably,the displacement per cycle is somewhat less than the width of the blade.

When the blade reciprocates at high speed and also advances along thepath P at a high programmed feed rate, there is little danger that theheat generated between the reciprocating blade and the sheet materialwill cause local hotspots and fusion between the plies of the layup oracross the line of cut.

Since the angle in the cutting path at point A is larger than apredetermined angle, for example 30, the cutting blade 14 can not movecontinuously around the corner without exceeding the capabilities of theequipment. It, therefore, is necessary to stop the advancement of theblade adjacent point A, lift the blade out of the sheet material androtate the blade about the 0-axis into alignment with the next segmentAB of the path P before the blade continues along the path P. A methodof executing such an operation with automatic lifting is described ingreater detail in a co-pending application Ser. No. 183,107, filed Sept.23, 1971 entitled Method for Cutting Sheet Material and for GeneratingRelated Controller Commands and having the same assignee as the presentinvention. If the blade were allowed to reciprocate at a high strokingspeed before it is withdrawn and after it plunges back into the layupmaterial, it is possible that fusion of the sheet material could occurin the vicinity of the point A. in accordance with the present inventionthe programmed stroking speed of the stroking motor is reduced to avalue that does not generate excessive heat and the cornering operationis then executed without difficulty.

The programmed feed rate for the relatively short segment AB issignificantly smaller than the maximum because the carriages l6 and 18would not achieve maximum speed and, if they attempted to achievemaximum speed, there would be extensive strain and wear to themechanical components and drive motors of the cutting system. inaccordance with the present invention, the basic commands from the tape22 prescribe a reduced feed rate and correspondingly a reduced strokingspeed which is suitable for short displacements of the blade less than apredefined amount. The rate of advancement and the stroking speed may,for example, be made proportional to the length of the cutting pathsegment AB. When the blade reaches point B it is lifted and rotated asat point A because the change in direction of the cutting path is,again, too large to be executed by merely rotating the blade in thelayup.

The segment BC of the cutting path is a curved segment having arelatively small radius which, it will be assumed, cannot be traversedat the maximum feed rate due to inertial loads and other inherentlimitations of the cutting system. Furthermore, the accuracy with whichthe cutting blade tracks a desired line of cut depreciates where thefeed rate is within the capacity of the system but, because of thecontour of the line of cut and the rapid movement, deviations from thecutting path become intolerably large. Accordingly, the feed rate of thecutting blade defined by the tape program is reduced to maintainaccurate tracking and, at the same time, the stroking speed of the bladeis reduced to prevent fusion. When the blade reaches point C, however, amaximum feed rate command and a new stroking speed command are read bythe controller 20 so that the blade then proceeds at high speed alongthe generally linear segment of the cutting path beyond point C.

in accordance with the above description, it will be apparent that amethod of cutting a layup of sheet material is disclosed in which thestroking speed of the cutting blade is regulated in accordance with thefeed rate along the cutting path and the feed rate is in turn determinedprimarily by the contour of the cutting path. The implementation of thismethod in hardware can be achieved by several means. As described above,the feed rate and the stroking speed commands are separately programmedon the memory tape 22 for processing by the controller 20 during thecutting operation. An entire data processing system which is capable ofgenerating programs containing both the feed rate and stroking speedcommands is shown in FIG. 4.

The cutting program is first established by preparing a marker 80.0rlayout bearing the outlines of the pattern pieces arranged in the samemanner that they will be cut from the layup. The marker is then placedon a digitizer 82 and the peripheries of the individual pattern piecesare traced either manually or by an automatic line follower so thatpoint data defining the peripheries is generated as a series of digitswhich may be either transmitted directly to a data processor 84 orrecorded on a tape for subsequent use by the data processor.

The data processor 84 is preferably a stored program computer whichreceives the point data and generates the cutting program as a series ofbasic commands intelligible to the controller 20. The basic commands aretransmitted from the processor 84 to a recorder 86 which prints thecommands on an initially blank memory tape 22. The tape is theninstalled in the tape reader of the controller 20 and the basic commandsfrom the tape are translated into control signals that are transmittedduring the cutting operation to the cutting mechanism 88 comprised ofthe drive motors, carriages, cutting table and blade of the apparatus 10in FIG. 1.

When the data processor 84 receives the digitized point data, the storedprogram within the processor determines the feed rate and strokingspeeds which are compatible with the cutting mechanism 88 and generatesbasic commands for the blank memory tape accordingly. FIG. is a flowdiagram of one stored program subroutine for generating the feed rateand stroking speed commands. The entry point 94) of the subroutinereceives input information including the digitized point data as acutting program is generated. The firt matter determined in thesubroutine is whether the cutting blade is up and out of engagement withthe layup as indicated by block 92. if the blade is up, a reducedstroking speed command is caused to be recorded on the blank programtape as indicated at block 94. A reduced stroking speed when the bladeis out of the layup reduces wear on the blade and the supportingcomponents while no productive cutting is being accomplished. Thereduced stroking speed is derived from one of several parameter cards 95which are inserted into the data processor before the processor isstarted and which are imposed with the various pieces of informationillustrated, including the reduced stroking speed desired when the bladeis out of the layup. As shown at block 96, another matter determinedwhen the blade is out of the layup is whether the displacement AX, AY isless than a predefined mount AD for example one inch, also derived froma parameter card. Even when the blade is out of the layup, it isdesirable to reduce the translation rate or feed rate below the maximumrate when very short displacements are desired so that strain and wearon the cutting mechanism are reduced. if the displacement is greaterthan one inch, no feed command is given and the subroutine is thenexited at block 98 without producing a basic command related to the feedrate. However, if the displacement is less than an inch, the feed ratecommanded is proportional to AX, AY as indicated at block 104) and thesubroutine is exited at block M1 2. It will be assumed that unless afeed rate command is recorded on the tape, the carriages l6 and 18 movethe blade at the maximum feed rate.

If the blade 14 is down and in cutting engagement with the sheetmaterial, a different logic path is followed as indicated at block 92.it has been mentioned with respect to the traversal of the cutting pathP in FIG. 3 that several considerations relating to the geometry of thecutting path influence the rate at which the blade advances along thecutting path. One of these considerations is represented at block 104.If, as shown at point A in FIG. 3, the change in direction is greaterthan a preselected amount A taken from a parameter card, which requireslifting the blade, the feed is stopped and reduced stroking speedpreviously recorded on the parameter cards is imposed on the programtape to reduce the stroking speed until after the corner has beenexecuted by the cornering subroutine concerning the lifting and rotationof the blade. The cornering subroutine may also provide aresume-stroking-speed-and-feed command to revert the feed rate andstroking speed to the maximums, assuming other conditions such as thelength of the next segment are consistent with such command. if the feedis stopped and a reduced stroking speed command is generated at block106, the subroutine is exited at block 108.

If the change in direction is less than A and, therefore, lifting androtation of the blade are not necessary, further considerations bearingupon the feed rate and stroking speed are examined. In block 110consideration is given to the length of the subsequent path segment andif this segment is less than a preselected amount AD such as one inch,taken from the parameter cards, a reduced feed rate and stroking speedproportional to AX, AY are outputed on the memory tape and thesubroutine is exited at block 114 in much the same manner as the programwas generated at blocks and 102.

Assuming still further that the conditions of blocks 104 and are notpresent, a further consideration concerning the subsequent segment ofthe cutting path is examined in view of the hardware limitations on theparameter cards as indicated at block 116. If for example the cuttingblade is at point B in the cutting path of FIG. 3, a reduced feed rateand stroking speed along the path segment having the relatively smallradius of curvature may be necessary in order to maintain accuracy andto stay within the capabilities of the hardware. Both the desired feedrate and stroking speed are derived from the information previouslyinserted in the data processor 3d on the parameter cards and the reducedrate and speed are commanded as indicated at block 118 before theroutine is exited at block 120. It will be recognized that the strokingspeeds commanded at blocks 106 and 1 18 may be the same or differentdepending upon the conditions that are to be satisfied as the bladeadvances along the cutting path.

If none of the conditions specified in blocks 104, 110 and 116 are metwhen the blade is down, the subroutine is exited at block 122 and withno feed or speed commands programmed on the tape, the cutting blade willmove along the cutting path at the maximum feed rate and a correspondingstroking speed.

In this manner a program tape bearing both feed rate commands andstroking commands is generated by the data processor 84 and recorder 86When the controller 20 reads the basic commands from the program tapethe cutting mechanism 88 causes the blade I4 to advance along thecutting path at variable feed rates and regulated stroking speeds in acutting operation that is optimized to provide maximum utilization ofthe hardware without overheating or fusing the sheet material. While thevariation of feed rates and stroking speeds is governed principally bythe contour of the cutting path, the stroking speed generally changeswith the feed rate. If the feed rate increases, the stroking speed alsoincreases but notnecessarily in a proportional relationship since thedisplacement of the blade during one reciprocation cycle of the bladeneed not necessarily remain constant at all feed rates. In the samemanner if the feed rate is reduced, the stroking speed is generallyreduced also, although not necessarily in a proportional relationship.

FIG. 6 illustrates one embodiment of the cutting mechanism which isdesigned to operate from a memory tape which contains both feed rate andstroking speed commands programmed, for example, as described withrespect to FIGS. 41 and 5. The controller 20 is connected to an Xcarriage motor drive 130, a Y carriage motor driver 132 and a -motordriver 134 to transmit motion commands for the cutting blade 14. The Xdriver 130 energizes the X drive motor 44 and in a corresponding mannerthe Y driver 132 energizes the Y driver motor 54 so that the composite Xand Y motions produced by the motors 44 and 54 cause the blade to betranslated to any point over the table I2. In the same manner and at thesame time the O-driver 134 energizes the 6-drive motor 64 to rotate thecutting blade and align it with the direction of the cutting path,assuming that the blade 14 is lowered into cutting engagement with thelayup of sheet material. In accordance with the present invention, thecontroller also receives stroking speed commands from the programmedtape and applies stroking speed control signals to a stroke driver 136.The driver 136 is in turn connected to the stroking motor 70 andenergizes the motor in accordance with the speed commands derived fromthe programmed tape.

FIG. 7 shows a modified embodiment of the present invention whichoperates independently of any stroking speed commands on a memory tapeor which operates from tapes which contain no stroke speed information.In this embodiment of the invention only X-,Y- and 0-motion commands aretransmitted from the controller 20 to the respective drivers I30, I32and 134. The drivers energize their respective motors to produce thedesired movement of the cutting blade 14 through the layup of sheetmaterial in the same manner that the blade 14 is moved in the embodimentof FIG. 6. In FIG. 7, however, feed rate information is derived from theX and Y motion commands by an X feed rate tachometer 140 and a Y feedrate tachometer 142. With the feed rates along the principalcoordinatesof motion of the cutting blade 14, a shaper circuit 144calculates the composite feed rate, and a stroking speed signaldetermined in accordance with the composite feed rate is applied to thestroke driver 136 to regulate the reciprication speed of the strokingmotor 70. The shaper circuit M4 may provide a selected minimum strokingspeed at all times in order to execute sharp corners such as shown atpoint A in FIG. 3. The shaper may also be adjustable or be provided witha variable program so that the feed rate and stroking speed relationshipcan be varied for cutting different types of materials, some of whichare more sensitive to heat than others.

While the present invention has been described in several preferredembodiments it should be understood that further modifications andsubstitutions can be had in both the steps of the method and componentsof the apparatus without departing from the spirit of the invention. Inparticular, the stroking speeds may be varied in magnitude by finiteamounts by establishing a schedule of preselected stroking speeds forvarious feed rates and other cutting conditions along the line of cut.Alternatively, the speed rates may be regulated according to aninfinitely variable schedule of stroking speeds so that the strokingspeed of the cutting blade can be varied in a continuous manner as thecutting path requires. The above-described embodiments utilize avariable speed stroking motor and a fixed length stroke to change thestroking speed of the blade; however, the present invention can also bepracticed by maintaining a constant reciprocation rate and varying theradius of the crank that produces the reciprocating motion. Although thevariable motor speed results in a less complicated structure and istherefore preferred from a design standpoint, reduction of the bladestroke while maintaining a constant reciprocation speed will also resultin generation of less heat between the blade and the sheet material.Still further, it is contemplated that cutting systems employing both avariable speed stroking motor and a variable stroke drive linkage can beutilized to practice the present invention. It is therefore apparentthat the use of the term stroking speed refers not exclusively to thereciprocation rate of the cutting blade but encompasses the reducedrelative velocity of the cutting blade and sheet material whichaccompanies a reduction in the length of the blade stroke. Accordingly,the present invention has been described in several preferredembodiments merely by way of illustration rather than limitation.

I claim:

1. Apparatus for cutting sheet material comprising: support meansproviding a work surface for holding sheet material to be cut in aspread condition; a reciprocating cutting tool in the form of a cuttingblade having a sharpened cutting edge extending along one edge of theblade; controlled drive means connecting with the tool and the supportmeans for advancing the tool and sheet material spread on the worksurface relative to one another with the cutting edge of the bladegenerally perpendicular to and in cutting engagement with the sheetmaterial; stroking means including an adjustable speed drive motorconnected with the reciprocating cutting tool for drawing the cuttingedge of the blade in cutting engagement with the sheet materialcyclically in and out of the material at an adjustable speed as the tooland sheet material move relative to one an- L11" other; and. strokingcontrol means including a motor driver connected to the adjustable speeddrive motor of the-stroking means and operatively associated with thecontrolled drive mean's for regulating the adjustable speed at which thecutting edge is cyclically drawn in and out of the sheet material as afunction of the rate at which the controlled drive means advances thetool and the sheet material relative to one-another.

2. Apparatus as defined in claim 1 wherein the stroking control meansand the controlled drive means include a common program tape containingboth feed rate information defining the rate at which the tool andthesheet material advance relative to one another and stroking speedinformation, the information providing increased stroking speeds atincreased feed rates.

3. Apparatus as defined in claim 1 wherein the stroke control meansincludes rate sensing means for producing regulating signals inaccordance with the rate of advancement of the tool and the sheetmaterial relative .to

one another.

4. A method of cutting a layup of sheet material along a cutting pathdefining a pattern piece with a reciprocating cutting blade having acutting edge extending in the direction ofreciprocation comprising:moving the reciprocating cutting blade and the layup relative to oneanother at a controlled feed rate to guide the cutting edge of the bladealong the cutting path in cutting engagement with the layup; rotatingthe reciprocating cutting blade about an-axis extending in the samedirection as the cutting edge to maintain the blade generally alignedwith the direction of cut along the cutting path; and regulating thestroking speed of the reciprocating cutting blade as the blade is movedalong the cutting path by increasing the stroking speed with increasingcontrolled feed rates in accordance with a predetermined schedule anddecreasing the stroking speed with decreasing controlled feed rates alsoin accordance with a predetermined schedule.

5. A method of cutting a layup of sheet material as defined by claim 4including the additional step of maintaining the length of thereciprocation stroke constant at each point along the cutting pathdefining the pattern piece.

6. A method of cutting a layup of sheet material as defined in claim 4wherein the step of regulating includes establishing the samepredetermined schedule of preselected stroking speeds varying inmagnitude by finite amounts for both increasing and decreasingcontrolled feed rates, and changing the stroking speeds of thereciprocating cutting blade by finite amounts in accordance with saidsame schedule to achieve the preselected stroking speeds.

7. A method of cutting a layup of sheet material as defined in claim 4wherein the step of regulating comprises establishing one infinitelyvariable schedule of stroking speeds for both increasing and decreasingcontrolled feed rates, and changing the stroking speed of thereciprocating cutting blade in a continuous manner in accordance withthe one infinitely variable schedule to achieve various stroking speedsduring the cutting operation.

8. A method of cutting pattern pieces from sheet ma terial comprising:defining a desired line of cut in the sheet material in accordance withthe pattern piece desired; providing a cutting blade having a cuttingedge extending along an edge portion of the blade; plunging the cuttingblade into and through the sheet material to position the cutting edgein generally perpendicular relationship to the sheet material; movingthe cutting blade and the sheet material relative to one another in acontrolled manner to advance the cutting edge forward of the blade alongthe desired line of cut; cyclically stroking the cutting blade relativeto the sheet material in a direction parallel with the cutting edge asthe cutting edge advances along the desired line of cut; and controllingthe stroking speed of the cutting blade as the cutting edge advancesalong the line of cut to coordinate the stroking speed and speed ofmovement along the line of cut by increasing the stroking speed withincreasing speed of movement and decreasing the stroking speed withdecreasing speed of movement.

9. A method of cutting pattern pieces as defined in claim 8 includingthe step of maintaining the stroke of the blade constant as the strokingspeed varies.

l0.A method of cutting pattern pieces as defined in claim 8 wherein thestep of controlling comprises changing the length of the stroke of theblade to achieve desired stroking speeds of the cutting edge.

11. A method of cutting pattern pieces as defined in claim 8 wherein thesteps of moving and controlling comprise adjusting the speed of movementand the stroking speed of the cutting blade at different points alongthe line of cut in accordance with the line geometry.

12. The method of claim 11 wherein the step of adjusting moreparticularly comprises reducing the speed of movement and the strokingspeed of the blade at

1. Apparatus for cutting sheet material comprising: support meansproviding a work surface for holding sheet material to be cut in aspread condition; a reciprocating cutting tool in the form of a cuttingblade having a sharpened cutting edge extending alonG one edge of theblade; controlled drive means connecting with the tool and the supportmeans for advancing the tool and sheet material spread on the worksurface relative to one another with the cutting edge of the bladegenerally perpendicular to and in cutting engagement with the sheetmaterial; stroking means including an adjustable speed drive motorconnected with the reciprocating cutting tool for drawing the cuttingedge of the blade in cutting engagement with the sheet materialcyclically in and out of the material at an adjustable speed as the tooland sheet material move relative to one another; and stroking controlmeans including a motor driver connected to the adjustable speed drivemotor of the stroking means and operatively associated with thecontrolled drive means for regulating the adjustable speed at which thecutting edge is cyclically drawn in and out of the sheet material as afunction of the rate at which the controlled drive means advances thetool and the sheet material relative to one another.
 2. Apparatus asdefined in claim 1 wherein the stroking control means and the controlleddrive means include a common program tape containing both feed rateinformation defining the rate at which the tool and the sheet materialadvance relative to one another and stroking speed information, theinformation providing increased stroking speeds at increased feed rates.3. Apparatus as defined in claim 1 wherein the stroke control meansincludes rate sensing means for producing regulating signals inaccordance with the rate of advancement of the tool and the sheetmaterial relative to one another.
 4. A method of cutting a layup ofsheet material along a cutting path defining a pattern piece with areciprocating cutting blade having a cutting edge extending in thedirection of reciprocation comprising: moving the reciprocating cuttingblade and the layup relative to one another at a controlled feed rate toguide the cutting edge of the blade along the cutting path in cuttingengagement with the layup; rotating the reciprocating cutting bladeabout an axis extending in the same direction as the cutting edge tomaintain the blade generally aligned with the direction of cut along thecutting path; and regulating the stroking speed of the reciprocatingcutting blade as the blade is moved along the cutting path by increasingthe stroking speed with increasing controlled feed rates in accordancewith a predetermined schedule and decreasing the stroking speed withdecreasing controlled feed rates also in accordance with a predeterminedschedule.
 5. A method of cutting a layup of sheet material as defined byclaim 4 including the additional step of maintaining the length of thereciprocation stroke constant at each point along the cutting pathdefining the pattern piece.
 6. A method of cutting a layup of sheetmaterial as defined in claim 4 wherein the step of regulating includesestablishing the same predetermined schedule of preselected strokingspeeds varying in magnitude by finite amounts for both increasing anddecreasing controlled feed rates, and changing the stroking speeds ofthe reciprocating cutting blade by finite amounts in accordance withsaid same schedule to achieve the preselected stroking speeds.
 7. Amethod of cutting a layup of sheet material as defined in claim 4wherein the step of regulating comprises establishing one infinitelyvariable schedule of stroking speeds for both increasing and decreasingcontrolled feed rates, and changing the stroking speed of thereciprocating cutting blade in a continuous manner in accordance withthe one infinitely variable schedule to achieve various stroking speedsduring the cutting operation.
 8. A method of cutting pattern pieces fromsheet material comprising: defining a desired line of cut in the sheetmaterial in accordance with the pattern piece desired; providing acutting blade having a cutting edge extending along an edge portion ofthe blade; plunging the cutting blade iNto and through the sheetmaterial to position the cutting edge in generally perpendicularrelationship to the sheet material; moving the cutting blade and thesheet material relative to one another in a controlled manner to advancethe cutting edge forward of the blade along the desired line of cut;cyclically stroking the cutting blade relative to the sheet material ina direction parallel with the cutting edge as the cutting edge advancesalong the desired line of cut; and controlling the stroking speed of thecutting blade as the cutting edge advances along the line of cut tocoordinate the stroking speed and speed of movement along the line ofcut by increasing the stroking speed with increasing speed of movementand decreasing the stroking speed with decreasing speed of movement. 9.A method of cutting pattern pieces as defined in claim 8 including thestep of maintaining the stroke of the blade constant as the strokingspeed varies.
 10. A method of cutting pattern pieces as defined in claim8 wherein the step of controlling comprises changing the length of thestroke of the blade to achieve desired stroking speeds of the cuttingedge.
 11. A method of cutting pattern pieces as defined in claim 8wherein the steps of moving and controlling comprise adjusting the speedof movement and the stroking speed of the cutting blade at differentpoints along the line of cut in accordance with the line geometry. 12.The method of claim 11 wherein the step of adjusting more particularlycomprises reducing the speed of movement and the stroking speed of theblade at changes in direction of the line of cut.